Robotically applied hardfacing with pre-heat

ABSTRACT

A system and method for the automated or “robotic” application of hardfacing to a surface of a drill bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of the present application is related to subject matter disclosed in U.S. patent application Ser. No. 12/257,219, filed Oct. 23, 2008, now U.S. Pat. No. 8,450,637, issued May 28, 2013, for APPARATUS FOR AUTOMATED APPLICATION OF HARDFACING MATERIAL TO DRILL BITS. The subject matter of the present application is also related to subject matter disclosed in U.S. patent application Ser. No. 12/603,734, filed Oct. 22, 2009, now U.S. Pat. No. 8,948,917, issued Feb. 3, 2015, for SYSTEMS AND METHODS FOR ROBOTIC WELDING OF DRILL BITS.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for the application of hardfacing to portions of a drill bit using robotic apparatus.

2. State of the Art

In the exploration of oil, gas, and geothermal energy, wells or boreholes in the earth are created in drilling operations using various types of drill bits. These operations typically employ rotary and percussion drilling techniques. In rotary drilling, the borehole is created by rotating a drill string having a drill bit secured to its lower end. As the drill bit drills the well bore, segments of drill pipe are added to the top of the drill string. While drilling, a drilling fluid is continually pumped into the drilling string from surface pumping equipment. The drilling fluid is transported through the center of the hollow drill string and through the drill bit. The drilling fluid exits the drill bit through one or more nozzles in the drill bit. The drilling fluid then returns to the surface by traveling up the annular space between the well bore and the outside of the drill string. The drilling fluid transports cuttings out of the well bore as well as cooling and lubricating the drill bit.

The type of drill bit used to drill the well will depend largely on the hardness of the formation being drilled. One type of rotary rock drill is a drag bit. Early designs for a drag bit included hardfacing applied to various portions of the bit. Currently, designs for drag bits have extremely hard cutting elements, such as natural or synthetic diamonds, mounted to a bit body. As the drag bit is rotated, the cutting elements form the bottom and sides of the well bore.

Another typical type of rotary drill bit is the tri-cone roller drill bit that has roller cones mounted on the body of the drill bit, which rotate as the drill bit is rotated. Cutting elements, or teeth, protrude from the roller cones. The angles at which the roller cones are mounted are mounted on the bit body determine the amount of cut or bite of the bit with respect to the well bore. As the roller cones of the drill bit roll on the bottom of the hole being drilled, the teeth or carbide inserts apply a high compressive and shear loading to the formation causing fracturing of the formation into debris. The cutting action of roller cones comprises a combination of crushing, chipping and scraping. The cuttings from a roller cone drill bit typically comprise a mixture of chips and fine particles.

Yet another type of rotary drill bit is a hybrid drill bit that has a combination of hard cutting elements, such as natural or synthetic diamonds and roller cones mounted on the body of the drill bit.

There are two general types of roller cone drill bits; TCI bits and steel-tooth bits. “TCI” is an abbreviation for tungsten carbide insert. TCI roller cone drill bits have roller cones having a plurality of tungsten carbide or similar inserts of high hardness that protrude from the surface of the roller cone. Numerous styles of TCI drill bits are designed for various types of formations, in which the shape, number and protrusion of the tungsten carbide inserts on the roller cones of the drill bit will vary, along with roller cone angles on the drill bit.

Steel-tooth roller cone drill bits are also referred to as milled-tooth bits because the steel teeth of the roller cones are formed by a milling machine. However, in larger bits, it is also known to cast the steel teeth and, therefore, “steel-tooth” is the better reference. A steel-tooth roller cone drill bit uses roller cones each having an integral body of hardened steel with teeth formed on the periphery. There are numerous styles of steel-tooth roller cone drill bits designed for formations of varying hardness in which the shape, number and protrusion of the teeth will vary, along with roller cone angles on the drill bit.

The cost efficiency of a drill bit is determined by the drilling life of the drill bit and the rate at which the drill bit penetrates the earth. Under normal drilling conditions, the teeth of the steel-tooth roller cone drill bits are subject to continuous impact and wear because of their engagement with the rock being drilled. As the teeth are worn away, the penetration rate of the drill bit decreases causing the cost of drilling to increase.

To increase the cost efficiency of a steel-tooth roller cone drill bit or a hybrid drill bit having steel-tooth roller cones, it is necessary to increase the wear resistance of the steel teeth. To accomplish this, it is known to deposit one or more layers of a wear-resistant material or “hardfacing” to the exposed surfaces of the steel teeth. Fusion hardfacing refers to a group of techniques that apply (fuse) a wear-resistant alloy (hardfacing) to a substrate metal. Common hardfacing techniques include arc welding and gas torch welding, among other welding processes.

Conventional welding techniques used to apply hardfacing to steel-tooth roller cone drill bits include oxyacetylene welding (OAW) and atomic hydrogen welding (AHW). Currently, manual welding is typically used in the commercial production of roller cone rock bits. Roller cones are mounted on a positioning table while a welding torch and welding rod are used to manually apply hardfacing to portions of each tooth of each roller cone by a welder moving from tooth to tooth and cone to cone from various positions.

Conventional hardfacing materials used to add wear resistance to the steel teeth of a roller cone drill bit include tungsten carbide particles in a metal matrix, typically cobalt or a mixture of cobalt and other similar metals. Many different compositions of hardfacing material have been employed in the rock bit field to achieve wear-resistance, durability and ease of application. Typically, these hardfacing materials are supplied in the form of a welding rod, but can be found in powder form for use with other types of torches.

The physical indicators for the quality of a hardfacing application include uniformity, thickness, coverage, porosity, and other metallurgical properties. Typically, the skill of the individual applying hardfacing determines the quality of the hardfacing. The quality of hardfacing varies between drill bits as well as between the roller cones of a drill bit, and individual teeth of a roller cone. Limited availability of qualified welders has aggravated the problem because the application of hardfacing is extremely tedious, repetitive, skill-dependent, time-consuming, and expensive. The application of hardfacing to roller cones is considered the most tedious and skill-dependent operation in the manufacture of a steel-toothed roller cone drill bit. The consistency of the application of hardfacing to a drill bit by a skilled welder varies over different portions of the drill bit.

When attempts to utilize robotics to automate the welding process were made, the same configuration was used having a robotic arm to replace the human operator's arm and its varied movements, while leaving the roller cone on a positioning table. The positioning table is capable of automatic indexing between teeth and rows of teeth of a roller cone.

Further, the ability of hardfacing to bond to a drill bit is affected by the temperature of the drill bit when the hardfacing is applied. The hotter the drill bit during hardfacing the better the hardfacing bonds to the drill bit. Also, the hotter the drill bit when hardfacing is applied, the risk for cracking of the drill bit during hardfacing is reduced.

BRIEF SUMMARY OF THE INVENTION

A system and method for the application of hardfacing to surfaces and components of drill bits, components of drill bits, and downhole tools at elevated temperature levels are disclosed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements.

The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.

FIG. 1 is a side view of a steel-tooth roller cone drill bit.

FIG. 1A is a side elevational view of an earth-boring drill bit according to an embodiment of the present invention.

FIG. 1B is a side elevational view of a drag-type earth-boring drill bit according to an embodiment of the present invention.

FIG. 2 is an isometric view of a typical steel-tooth cutter such as might be used on the steel-tooth roller cone drill bit of FIG. 1.

FIG. 2A is a partial sectional view of another embodiment of a rotatable cutter assembly, including a cone, of the present invention and that may be used with the earth-boring drill bit shown in FIG. 1A.

FIG. 2B is a sectional view of another embodiment of a unitary cutter assembly, including a cone, of the present invention and that may be used with the earth-boring drill bit shown in FIG. 1A.

FIG. 3 is an isometric view of a typical steel-tooth such as might be located on the steel-tooth cutter of FIG. 2.

FIG. 4 is an isometric view of the steel-tooth of FIG. 3 after hardfacing has been applied.

FIG. 5 is a schematic of a preferred embodiment of a robotic welding system using a preheated cone of the present invention.

FIG. 5A is a schematic of another embodiment of the robotic welding system using a preheated cone of the present invention.

FIG. 6 is an isometric view of a robot manipulating a cutter to be hardfaced.

FIG. 7 is an isometric view of a cutter positioned beneath a torch in preparation for the application of hardfacing.

FIG. 8 is an isometric view of a chuck of the preferred type attached to the end of the robot.

FIG. 9 is an isometric view of a jaw for a three-jaw chuck specially profiled to include a journal land and a race land for gripping a rolling cutter.

FIG. 10 is a schematic side view of a positioner and a torch.

FIG. 11 is a schematic cross-section of the torch.

FIG. 12 is a cross-section of a torch configured in accordance with a preferred embodiment.

FIG. 13 is an isometric view illustrating a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the outer ends of the teeth.

FIG. 13A is an isometric view illustrating a robot manipulating the torch and a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the outer ends of the teeth.

FIG. 14 is a side view illustrating a torch applying hardfacing to the outer end of a tooth on the outer row of the cutter.

FIG. 15 is a side view illustrating the torch applying hardfacing to the leading flank of a tooth on the outer row of the cutter.

FIG. 16 is an isometric view illustrating a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the inner end of a tooth on the cutter.

FIG. 17 is a bottom view of a typical steel-tooth such as might be located on the steel-tooth cutter of FIG. 2, illustrating a substantially trapezoidal waveform target path for hardfacing in accordance with a preferred embodiment of the present invention.

FIG. 18 is a schematic representation of the oscillation of the torch on axis of oscillation “AO” having an oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention.

FIG. 19 is a schematic representation of a substantially triangular waveform torch path for hardfacing in accordance with a preferred embodiment of the present invention.

FIG. 20 is a schematic representation of a waveform created by oscillation of the cutter relative to the intersection of the target path and the oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention.

FIG. 21 is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of FIG. 20.

FIG. 22 is a schematic representation of a generally rectangular shaped waveform created by oscillation of the cutter relative to the intersection of the target path and the oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention.

FIG. 23 is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of FIG. 22.

FIG. 24 is a schematic representation of a “shingle” pattern of hardfacing applied to a tooth of a cutter, in accordance with a preferred embodiment of the present invention.

FIG. 25 is a schematic representation of a “herringbone” pattern of hardfacing applied to a tooth of a cutter, in accordance with a preferred embodiment of the present invention.

FIG. 26A is a cross-section of the cone illustrated in FIG. 2A having hardfacing thereon.

FIG. 26B is a cross-section of the cone illustrated in FIG. 2B having hardfacing thereon.

FIG. 27 is a side elevational view of a drag-type earth-boring bit according to an embodiment of the present invention having hardfacing applied to portions thereof.

DETAILED DESCRIPTION OF THE INVENTION

The system and method of the present invention use a robotic system having a plasma transfer arc torch secured to a torch positioner to apply hardfacing to a component of the drill bit, drill bit, or downhole tool at an elevated temperature level. The torch positioner is program-controllable in a vertical plane. Shielding, plasma, and transport gases are supplied to the torch through electrically or manually controllable flow valves. For handling a roller cone, a robot having program controllable movement of an articulated arm is used. A chuck adapter is attached to the arm of the robot. A three-jaw chuck is attached to the chuck adapter. The chuck is capable of securely holding a roller cone in an inverted position or any desired position. The component of a drill bit or a drill bit may be pre-heated in an oven or furnace or may be continuously heated during applying hardfacing through the use of any suitable heating apparatus.

A first position sensor is positioned for determining the proximity of the torch and any localized heating apparatus to a surface of the roller cone, component of a drill bit, or drill bit. A second position sensor may be positioned for determining the location, orientation, or identification of the roller cone. A programmable control system is electrically connected to the torch, the torch positioner or robotic arm having the torch mounted thereon, the heating apparatus, the robot, shielding, plasma, and transport gas flow valves, and the position sensors for programmed operation of each. The robot is programmed to position a surface of a cutter below the torch prior to the application of welding material to the roller cone. The heating apparatus is used to maintain the temperature of the roller cone, component, or drill bit during the application of hardfacing for improved hardfacing of the roller cone, component, or drill bit.

Prior to the hardfacing of roller cones, components of drill bits, drill bits, and downhole tools, they are to be pre-heated to avoid cracking thereof and may continue to be heated during hardfacing to improve hardfacing bonding and minimize hardfacing deposit defects, and cracking. In this configuration, the torch is oscillated in a horizontal path. By controlling the cooling rate of the roller cone, component of a drill bit or downhole tool, or drill bit during hardfacing, the hardfacing exhibits a higher integrity deposit. The preheating of the roller cone, components of drill bits and downhole tools, and drill bits prior to hardfacing may occur by induction heating, heating immersed in a fluidized bed, resistance heating, radiative and convection heating, heating with an oxyacetylene torch, heating using natural gas, or heating in an inert environment. The heating of a roller cone, component of a drill bit, drill bit, or downhole tool during hardfacing may occur by heating with an oxyacetylene torch, heating using natural gas, radiative heating, and convection heating.

For instance, the preheated roller cone is manipulated such that a programmed target path for each tooth surface is followed beneath the path midpoint (or equivalent indicator) of the oscillating torch. The movement of the heating apparatus during hardfacing is programmed to maintain the overall temperature level of the roller cone, component of the drill bit, or drill bit and maintain the temperature level of the area of the roller cone, component of the drill bit, drill bit or downhole tool having hardfacing applied thereto. In one instance, the movement of the roller cone beneath the torch generates a waveform pattern of hardfacing, although any pattern may be used as desired. In an embodiment, the target path is a type of waveform path as well. Imposing the torch waveform onto the target path waveform generates a high-quality and efficient hardfaced coating on the roller cone. By further having the roller cone, the component of the drill bit, or the drill bit at an elevated temperature, the bond of the hardfacing to the roller cone, component of the drill bit, or drill bit is improved. In another embodiment, the roller cone is oscillated in relation to the torch as it follows the target path. This embodiment provides the ability to generate unique and desirable hardfacing patterns on the surface of the cutter, while maintaining symmetry and coverage, and through the use of maintaining the roller cone, component, or drill bit at an elevated temperature the quality of the hardfacing is improved.

An advantage of the system and method of the present invention is that it automates the hardfacing application of roller cones, components of the drill bits, a drill bit, or a downhole tool which increases the consistency and quality of the applied hardfacing, and thus the reliability, performance, and cost efficiency of the roller cone, component of the drill bit, the drill bit or downhole tool. Another advantage of the system and method of present invention is that it reduces manufacturing cost and reliance on skilled laborers. Another advantage of the system and method of the present invention is that by decreasing, in some circumstances, production time, product inventory levels can be reduced. Another advantage of the system and method of the present invention is that it facilitates the automated collection of welding data, from which further process controls and process design improvements can be made during the maintenance of the roller cone, component, or drill bit at an elevated temperature.

Another advantage of the system and method of the present invention is that utilization of the robotic arm to manipulate the roller cone, a robotic arm having the torch mounted thereon, and a robotic arm having the heating apparatus thereon improves the opportunity to integrate sensors for providing feedback. Another advantage of the system and method of the present invention is that utilization of the robotic arm to manipulate the roller cone provides the necessary surface-to-torch angularity for access, without disrupting the flow of the powder due to changes in the angle of the torch and a robotic arm to manipulate the heating apparatus improves the quality of the hardfacing applied to the roller cone, component, or drill bit.

As referred to hereinabove, the “system and method of the present invention” refers to one or more embodiments of the invention, which references are not intended to limit the language of the claims, or to be used to construe the claims. The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

FIG. 1 is a side view of a steel-tooth roller cone drill bit 1. The drill bit 1 has a plurality of steel-tooth roller cones 10. FIG. 2 is an isometric view of a typical steel-tooth roller cone 10 such as might be used on the drill bit of FIG. 1. Steel-tooth roller cone 10 has a plurality of rows of teeth 20. In FIG. 2, roller cone 10 has an inner row of teeth 12, an intermediate row of teeth 14, and an outer row of teeth 16. Each of rows of teeth 12, 14, and 16 has one or more teeth 20 therein.

FIG. 1A is a side elevational view of an earth-boring drill bit 510 according to another embodiment of the present invention. The earth-boring drill bit 510 includes a bit body 512 and a plurality of rotatable cutter assemblies 514. The bit body 512 may include a plurality of integrally formed bit legs 516. Threads 518 may be formed on the upper end of the bit body 512 for connection to a drill string (not shown). The bit body 512 may have nozzles 520 for discharging drilling fluid into a bore hole, which may be returned along with cuttings up to the surface during a drilling operation. Each of the rotatable cutter assemblies 514 include a cone 522 comprising a steel material and a plurality of cutting elements, such as the cutting inserts 524 shown. Each cone 522 may include a conical gage surface 526. Additionally, each cone 522 may have a unique configuration of cutting inserts 524 or cutting elements, such that the cones 522 may rotate in close proximity to one another without mechanical interference.

FIG. 1B illustrates a drill bit 610 incorporating a plurality of nozzle assemblies 630 therein. The drill bit 610 is configured as a fixed-cutter rotary full bore drill bit also known in the art as a drag bit. The drill bit 610 includes a crown or bit body 611 composed of steel body or sintered tungsten carbide body coupled to a support 619. The support 619 includes a shank 613 and a crossover component (not shown) coupled to the shank 613 to form a weld joint therebetween. The crossover component (not shown), which is manufactured from a tubular steel material, is coupled to the bit body 611 by pulsed MIG process to form a weld joint therebetween in order to allow the complex tungsten carbide material, when used, to be securely retained to the shank 613. It is recognized that the support 619, particularly for other materials used to form a bit body, may be made from a unitary material piece or multiple pieces of material in a configuration differing from the shank 613 being coupled to the crossover by weld joints as presented. The shank 613 of the drill bit 610 includes conventional male threads 612 configured to API standards and adapted for connection to a component of a drill string, not shown. A face 614 of the bit body 611 has mounted thereon a plurality of cutting elements 616, each comprising a polycrystalline diamond (PCD) table 618 formed on a cemented tungsten carbide substrate. The cutting elements 616, conventionally secured in respective cutter pockets 621 by brazing, for example, are positioned to cut a subterranean formation being drilled when the drill bit 610 is rotated under weight-on-bit (WOB) in a bore hole. The bit body 611 may include gage trimmers 623 including the aforementioned PCD tables 618 configured with a flat edge aligned parallel to the rotational axis of the bit (not shown) to trim and hold the gage diameter of the bore hole, and gage pads 622 on the gage which contact the walls of the bore hole to maintain the hole diameter and stabilize the bit in the hole.

During drilling, drilling fluid is discharged through nozzle assemblies 630 located in sleeve ports 628 in fluid communication with the face 614 of bit body 611 for cooling the PCD tables 618 of cutting elements 616 and removing formation cuttings from the face 614 of drill bit 610 into passages 615 and junk slots 617.

In FIG. 2, as shown by dashed lines, the interior of roller cone 10 of drill bit 1 of FIG. 1 includes a cylindrical journal race 40 and a semi-torus shaped ball race 42. Journal race 40 and ball race 42 are internal bearing surfaces that are finish machined after hardfacing 38 has been applied to teeth 20. FIG. 2A is a cross-sectional view illustrating one of the rotatable cutter assemblies 514 of the earth-boring drill bit 510 shown in FIG. 1A. As shown, each bit leg 516 may include a bearing pin 528. The cone 522 may be supported by the bearing pin 528, and the cone 522 may be rotatable about the bearing pin 528. Each cone 522 may have a central cone cavity 530 that may be cylindrical and may form a journal bearing surface adjacent the bearing pin 528. The cone cavity 530 may have a flat thrust shoulder 532 for absorbing thrust imposed by the drill string (not shown) on the cone 522. As illustrated in this example, the cone 522 may be retained on the bearing pin 528 by a plurality of locking balls 534 located in mating grooves formed in the surfaces of the cone cavity 530 and the bearing pin 528. Additionally, a seal assembly 536 may seal bearing spaces between the cone cavity 530 and the bearing pin 528. The seal assembly 536 may be a metal face seal assembly, as shown, or may be a different type of seal assembly, such as an elastomer seal assembly. Lubricant may be supplied to the bearing spaces between the cone cavity 530 and the bearing pin 528 by lubricant passages 538. The lubricant passages 538 may lead to a reservoir that includes a pressure compensator 540 (FIG. 1A).

As previously mentioned, the cone 522 may comprise a sintered particle-matrix composite material that comprises a plurality of hard particles dispersed through a matrix material. In some embodiments, the cone 522 may be predominantly comprised of the particle-matrix composite material.

The cutting inserts 524, lands 523, and bearing structures 568 may be formed from particle-matrix composite materials. The material composition of each of the cutting inserts 524, lands 523, bearing structures 568, and cone 522 may be separately and individually selected to exhibit physical and/or chemical properties tailored to the operating conditions to be experienced by each of the respective components. By way of example, the composition of the cutting inserts 524 and the lands 523 may be selected so as to form cutting inserts 524 comprising a particle-matrix composite material that exhibits a different hardness, wear resistance, and/or toughness different from that exhibited by the particle-matrix composite material of the cone 522.

The cutting inserts 524 and lands 523 may be formed from a variety of particle-matrix composite material compositions. The particular composition of any particular cutting insert 524 and the lands 523 may be selected to exhibit one or more physical and/or chemical properties tailored for a particular earth formation to be drilled using the drill bit 510 (FIG. 1A). Additionally, cutting inserts 524 and lands 523 having different material compositions may be used on a single cone 522.

By way of example, in some embodiments of the present invention, the cutting inserts 524 and the lands 523 may comprise a particle-matrix composite material that includes a plurality of hard particles that are harder than a plurality of hard particles of the particle-matrix composite material of the cone 522. The concentration of the hard particles in the particle-matrix composite material of the cutting inserts 524 and the lands 523 may be greater than a concentration of hard particles in a particle-matrix composite material of the cone 522.

FIG. 3 is an isometric view of a steel-tooth 20 located on steel-tooth roller cone 10 of FIG. 2. Tooth 20 has an included tooth angle of θ degrees formed at a vertex 36. Tooth 20 has a leading flank 22 and an opposite trailing flank 24. Leading flank 22 and trailing flank 24 are joined at crest 26, which is the top of tooth 20. A generally triangular outer end 28 is formed between leading flank 22, trailing flank 24, and crest 26. On the opposite side of tooth 20, a generally triangular inner end 30 is formed between leading flank 22, trailing flank 24, and crest 26. A base 32 broadly defines the bottom of tooth 20 and the intersection of tooth 20 with roller cone 10. Centerline 34 extends through crest 26 and base 32. Various alternatively shaped teeth on roller cone 10 may be used, such as teeth having T-shaped crests. Tooth 20 represents a common shape for a tooth, but the system and method of the present invention may be used on any shape of tooth.

To prevent early wear and failure of drill bit 1, it is necessary to apply an extremely wear-resistant material, or hardfacing 38, to surfaces 22, 24, 26, 28, and 30 of tooth 20. FIG. 4 is an isometric view of a typical steel-tooth 20 such having hardfacing 38 applied to surfaces 22, 24, 26, 28, and 30.

FIGS. 5 and 5A are schematic illustrations of the system of the present invention. Illustrated in FIG. 5 is a pre-heating device 1000 for a roller cone 10, component of a drill bit, drill bit or downhole tool, such as induction heating device, a resistance heating device, radiative and convection heating device, a device which heats with an oxyacetylene torch, a heating device using natural gas, or a heating device having an inert environment therein. Prior to the hardfacing of the roller cone, component of a drill bit or downhole tool, or drill bit, it is pre-heated in the pre-heating device 1000 to any desired temperature, such as in the range of 400° F. to 1,000° F., and this temperature can be maintained while applying the hardfacing. The roller cone, a component of a drill bit, or a downhole tool, is removed from the pre-heating device 1000 and transferred to the industrial robot 100 for the application of hardfacing thereto. The system further comprises an industrial robot 100 having a stationary base 102 and an articulated arm 104. Articulated arm 104 has an end 106 for holding during hardfacing a roller cone, component of a drill bit or downhole tool, or drill bit. Robot 100 has a plurality of axes of rotation 108 about which controllable movement permits wide-range positioning of distal end 106 relative to base 102. Robot 100 has six or more independently controllable axes of movement between base 102 and the distal end 106 of arm 104. FIG. 5A illustrates a drill bit 610 attached to the articulated arm 104, although drill bit 610 or drill bit 1 or portions of any drill bit may be attached to articulated arm 104 for the application of hardfacing to portions thereof.

Robot 100 has a handling capacity of at least 125 kg, and articulated arm 104 has a wrist torque rating of at least 750 nm. Examples of industrial robots that are commercially available include models IRB 6600/IRB 6500, which are available from ABB Robotics, Inc., 125 Brown Road, Auburn Hills, Mich., USA, 48326-1507.

An adapter 110 is attached to distal end 106. Adapter 110 has a ground connector 112 (see FIG. 7) for attachment to an electrical ground cable 114. A chuck 120 is attached to adapter 110. Chuck 120 securely grips roller cone 10 at journal bearing surface 40 and/or ball race 42, as shown in greater detail in FIGS. 8 and 9.

A thermal barrier, is provided between roller cone 10 and adapter 110 to prevent heat from causing premature failure of the rotating axis 108 at distal end 106 of articulated arm 104. The thermal barrier is an insulating spacer 116 (not shown) located between roller cone 10 and distal end 106 of robot 100. Alternatively, roller cone 10 may be gripped in a manner that provides an air space between roller cone 10 and distal end 106 of robot 100 to provide insulation.

A robot controller 130 is electrically connected to robot 100 for programmed manipulation of robot 100, including movement of articulated arm 104. An operator pendant 137 may be provided as electrically connected to robot controller 130 for convenient operator interface with robot 100. A sensor controller 140 is electrically connected to robot controller 130. Sensor controller 140 may also be electrically connected to a programmable logic controller 150.

A plurality of sensors 142 are electrically connected to sensor controller 140. Sensors 142 include a camera 144 and/or a contact probe 146. Alternatively, sensors 142 include a suitable laser proximity indicator 148 (illustrated as an arrow). Other types of sensors 142 may also be used. Sensors 142 provide interactive information to robot controller 130, such as the distance between a tooth 20 on roller cone 10 and torch 300.

A programmable logic controller 150 is electrically connected to robot controller 130. Programmable logic controller (PLC) 150 provides instructions to auxiliary controllable devices that operate in coordinated and programmed sequence with robot 100.

A powder dosage system 160 is provided for dispensing powder to the hardfacing system. A driver 162 is electrically connected to PLC 150 for dispensing the powder at a predetermined, desired rate.

A pilot arc power source 170 and a main arc power source 172 are electrically connected to PLC 150. A cooling unit 174 is electrically connected to PLC 150. In the preferred embodiment, a data-recording device is electrically connected to PLC 150.

A gas dispensing system 180 is provided. A transport gas source 182 supplies transport gas through a flow controller 184 to carry or transport hardfacing welding powder to torch 300. Flow controller 184 is electrically connected to PLC 150, which controls the operation of flow controller 184 and the flow and flow rate of the transport gas. A plasma gas source 186 supplies gas for plasma formation through a flow controller 188. Flow controller 188 is electrically connected to PLC 150, which controls the operation of flow controller 188 and the flow and flow rate of the plasma gas. Similarly, a shielding gas source 190 supplies shielding gas through a flow controller 192. Flow controller 192 is electrically connected to PLC 150, which controls the operation of flow controller 192 and the flow and flow rate of the shielding gas. It is known to utilize a single gas source for more than one purpose, e.g., plasma, shielding, and transport. Thus, different, multiple flow controllers connected in series alignment can control the flow and flow rate of gas from a single gas source.

The torch 300 comprises a plasma transferred arc (PTA) torch, that receives hardfacing welding powder from powder dosage system 160, and plasma, transport, and shielding gases from their respective supplies and controllers in gas dispensing system 180. Torch 300 is secured to a positioning table or positioner 200, which grips and manipulates torch 300. In the preferred embodiment, positioner 200 is capable of programmed positioning of torch 300 in a substantially vertical plane. The positioner 200 has a vertical drive 202 and a horizontal drive 204. Drives 202 and 204 may be toothed belts, ball screws, a toothed rack, pneumatic, or other means. If desired, an industrial robot 100 has six independently controllable axes of movement between base 102 and distal end 106 of arm 104. Having six independently controllable axes of movement between base 102 and distal end 106 of arm 104 as described herein may be used as the positioner 200 having the torch 300 mounted thereon.

Illustrated in FIG. 5A, is the system illustrated in FIG. 5 further including a robotic arm 100 having a suitable torch 100′ mounted on the distal end 106 thereof for selectively heating portions of the roller cone, component of a drill bit, drill bit or downhole tool held by the robotic arm 100 during the hardfacing thereof. The robotic arm 100 is connected to programmable logic controller 150 for the operation thereof and is supplied a suitable gas mixture from gas dispensing system 180. The torch 100′ is used to maintain the roller cone, component of a drill bit or downhole tool, or drill bit at any desired temperature level during the hardfacing operation to minimize cracking of the roller cone, component of a drill bit or downhole tool, or drill bit and to improve the bond of the hardfacing material to the roller cone, component of a drill bit or downhole tool, or drill bit. The robot 100 having torch 100′ is manipulated to heat any portion of the roller cone, component of a drill bit, drill bit, or downhole tool as required to maintain the temperature thereof at any desired level during hardfacing.

FIGS. 6 and 7 are isometric views of robot 100 shown manipulating roller cone 10 secured to adapter 110 on distal end 106 of articulated arm 104 of robot 100. As illustrated in FIG. 6 and in FIGS. 13-16, the several axes of rotation 108 provide sufficient degrees of freedom to permit vertical, horizontal, inverted, and rotated positioning of any tooth 20 of roller cone 10 directly beneath torch 300. As illustrated in FIG. 7, roller cone 10 is positioned beneath torch 300 in preparation for the application of hardfacing 38 (FIG. 4).

Adapter 110 is aligned by indicator with articulated arm 104. Adapter 110 is aligned to run substantially true with a programmable axis of movement of robot 100. A chuck 120 is attached to adapter 110 and indicator aligned to within 0.005 inch of true center rotation. Roller cone 10 is held by chuck 120 and also centered by indicator alignment. Roller cone 10 has grooves that permit location and calibration of the end of torch 300. Torch 300 electrode 304 (FIG. 11) is then used to align roller cone 10 about the z-axis of rotation of roller cone 10 by robot 100.

As illustrated in FIG. 7, electrical ground cable 114 is electrically connected to adapter 110 by ground connector 112, a rotatable sleeve connector. Alternatively, ground connector 112 is a brush connector. Ground cable 114 is supported by a tool balancer (not shown) to keep it away from the heat of roller cone 10 and the welding arc during hardfacing operations. Chuck 120 is attached to adapter 110. Roller cone 10 is held by chuck 120.

As roller cones 10 are manipulated vertically, horizontally, inverted, and rotated beneath torch 300, highly secure attachment of roller cone 10 to robot 100 is required for safety and accuracy of the hardfacing operation. Precision alignment of roller cones 10 in relation to chuck 120 is also necessary to produce a quality hardfacing and to avoid material waste.

FIG. 8 is an isometric view of the chuck 120, a three-jaw chuck, having adjustable jaws 122 for gripping a hollow interior of a roller cone 10. Jaws 122 are specially profiled to include a cylindrical-segment shaped journal land 124, which contacts journal race 40 on roller cone 10 (FIG. 2), providing highly secure attachment of roller cone 10 on chuck 120 of robot 100. A seal relief 128 is provided to accommodate a seal supporting surface on roller cone 10.

Illustrated in FIG. 9, jaws 122 are specially profiled to include a semi-torus shaped race land 126 above journal land 124. In this configuration, journal land 124 fits in alignment with journal race 40 and race land 126 fits in alignment with ball race 42 (FIG. 2), providing precise alignment against the centerline of ball race 42 and secure attachment of roller cone 10 on chuck 120 of robot 100. Seal relief 128 may be provided to accommodate a seal supporting surface on roller cone 10.

FIG. 10 is a schematic side view of positioner 200 and torch 300. As illustrated, positioner 200 has a clamp 206 for holding torch 300 in a secure and substantially vertical orientation. Vertical drive 202 provides controlled movement of torch 300 along the z-axis. Drive 203 connected to PLC 150 (FIGS. 5 and 5A) rotates the torch 300 of positioner 200 about the z-axis of a support 201. Drive 205 connected to the PLC 150 rotates torch 300 of positioner 200 about the z-axis of support 207. Drive 209 connected to the PLC 150 rotates torch 300 of positioner 200 about the y-axis of clamp 206. Horizontal drive 204 provides controlled movement of torch 300 along the y-axis. In combination, drives 202 and 204 provide controlled movement of torch 300 on a vertical plane. Drives 202 and 204 are electrically connected to PLC 150.

Drive 204 oscillates torch 300 along the horizontal y-axis in response to PLC 150 for programmed application of a wide-path bead of hardfacing 38 on the surface of teeth 20 (FIG. 4) of roller cone 10. Drive 202 moves torch 300 along the vertical z-axis in real-time response to measured changes in the voltage or current between torch 300 and roller cone 10. These occasional real-time distance adjustments maintain the proper energy level of the transferred arc between torch 300 and roller cone 10. The process can include measuring a voltage of a transferred arc between a torch electrode and the rolling cutter, communicating the voltage measurement data to a programmable logic controller, calculating a difference between the measured voltage and desired voltage, calculating an arc length adjustment needed to obtain the desired voltage, and actuating the torch positioner to vertically move the arc length adjustment. The torch can also be oscillated in a vertical direction to maintain a substantially constant voltage output of the torch.

Gas dispensing system 180 is connected by piping or tubing to torch 300 for the delivery of transport gas, plasma gas and shielding gas. Hardfacing powder is delivered to torch 300 within the stream of flowing transport gas, which receives the hardfacing powder from powder dosage system 160 (FIGS. 5 and 5A). Torch 300 is electrically connected to pilot arc power source 170 and main arc power source 172.

FIG. 11 is a schematic cross-section of torch 300. Torch 300 has a nozzle 302 that comprises a Plasma Transferred Arc (PTA) torch. A non-burning tungsten electrode (cathode) 304 is centered in nozzle 302 and a nozzle annulus 306 is formed between nozzle 302 and electrode 304. Nozzle annulus 306 is connected to plasma gas source 186 (FIG. 5) to allow the flow of plasma between nozzle 302 and electrode 304. A restricted orifice 314 accelerates the flow of plasma gas exiting nozzle 302. In this embodiment, nozzle annulus 306 is connected to powder dosage system 160 (not shown), which supplies hardfacing powder carried by transport gas to nozzle annulus 306.

Electrode 304 is electrically insulated from nozzle 302. A pilot arc circuit 330 is electrically connected to pilot arc power source 170 (FIG. 5), and electrically connects nozzle 302 to electrode 304. A main arc circuit 332 is electrically connected to main arc power source 172 (FIG. 5), and electrically connects electrode 304 to the anode work piece, roller cone 10. An insulator separates pilot arc circuit 330 and main arc circuit 332. Cooling channels 316 are provided in nozzle 302 for connection to a pair of conduits 176, 178 (FIG. 10) that circulate cooling fluid from cooling unit 174 (FIGS. 5 and 5A).

A gas cup 320 surrounds nozzle 302. Nozzle 302 is electrically insulated from gas cup 320. A cup annulus 322 is formed between gas cup 320 and nozzle 302. Cup annulus 322 is connected to shielding gas source 190 (FIGS. 5 and 5A) to allow the flow of shielding gas between gas cup 320 and nozzle 302.

A small, non-transferred pilot arc burns between non-melting (non-consumable) tungsten electrode 304 (cathode) and nozzle 302 (anode). A transferred arc burns between electrode 304 (cathode) and roller cone 10 (anode). Electrode 304 is the negative pole and roller cone 10 is the positive pole. Pilot arc circuit 330 is ignited to reduce the resistance to an arc jumping between roller cone 10 and electrode 304 when voltage is applied to main arc circuit 332. A ceramic insulator separates arc circuits 330 and 332.

Plasma Transferred Arc (PTA) welding is similar to Tungsten Inert Gas (TIG) welding. Torch 300 is supplied with plasma gas, shielding gas, and transport gas, as well as hardfacing powder. Plasma gas from plasma gas source 186 (FIGS. 5 and 5A) is delivered through nozzle 302 to electrode 304. The plasma gas exits nozzle 302 through orifice 314. When amperage from main arc circuit 332 is applied to electrode 304, the jet created from exiting plasma gas turns into plasma. Plasma gas source 186 is comprised of 99.9% argon (Ar).

Shielding gas from shielding gas source 190 is delivered to cup annulus 322. As the shielding gas exits cup annulus 322 it is directed towards the work piece, roller cone 10. The shielding gas forms a cylindrical curtain surrounding the plasma column, and shields the generated weld puddle from oxygen and other chemically active gases in the air. Shielding gas source 190 is 95% argon and 5% hydrogen, 100% argon, or argon and other gases.

Transport gas source 182 is connected to powder dosage system 160. Powder dosage system 160 (FIGS. 5 and 5A) meters hardfacing powder through a conduit connected to nozzle 302 at the proper rate for deposit. The transport gas from transport gas source 182 carries the metered powder to nozzle 302 and to the weld deposit on roller cone 10.

FIG. 12 is a cross-section of torch 300 wherein gas cup 320 of torch 300 has a diameter of less than 0.640 inch and a length of less than 4.40 inches. Nozzle 302 (anode) of torch 300 is made of copper and is liquid cooled. One such torch that is commercially available is the Eutectic E52 torch available from Castolin Eutectic Group, Gutenbergstrasse 10, 65830 Kriftel, Germany.

Gas cup 320 is modified from commercially available gas cups for use with torch 300 in that gas cup 320 extends beyond nozzle 302 by no more than approximately 0.020 inch. As such, gas cup 320 has an overall length of approximately 4.375 inches. As seen in the embodiment, transport gas and powder are delivered through a transport gas port 324 in nozzle 302. An insulating material is attached to the exterior of gas cup 320 of the torch 300 for helping to prevent short-circuiting and damage to torch 300.

The shielding of gas cup 320 described above is specially designed to improve shield gas coverage of the melt puddle for reducing the porosity thereof. This permits changing the orientation of gas cup 320 to nozzle (anode) 302 and reduction of shielding gas flow velocity. This combination significantly reduces porosity that results from attempts to use presently available commercial equipment to robotically apply hardfacing 38 to steel-tooth roller cones 10.

OPERATION OF THE INVENTION

Some of the problems encountered in the development of robotic hardfacing included interference between the torch and teeth on the roller cone, short circuiting the torch, inconsistent hardfacing powder flow, unsustainable plasma column, unstable puddle, heat buildup when using conventional welding parameters, overheated weld deposits, inconsistent weld deposits, miss-shaping of teeth, and other issues. As a result, extensive experimentation was required to reduce the present invention to practice.

As described herein, the system and method of the present invention begins with inverting what has been the conventional practice of roller cones. That is, the practice of maintaining roller cone 10 generally stationary and moving torch 300 all over it at various angles as necessary. Fundamental to the system and method of the present invention, torch 300 is preferably held substantially vertical, although it may be held at any angle or attitude desired through the use of a positioner 200 or robotic arm 100, while roller cone 10 is held by chuck 120 of robotic arm 104 and manipulated beneath torch 300. If torch 300 is robotically manipulated by positioner 200 or robotic arm 100 in varying and high angular positions relative to vertical, hardfacing powder in torch 300 will flow unevenly and cause torch 300 to become plugged. In addition to plugging torch 300, even flow of hardfacing powder is critical to obtaining a consistent quality bead of hardfacing material on roller cone 10. Thus, deviation from a substantially vertical orientation is avoided. Although, if plugging of torch 300 is not a problem with the particular hardfacing being used, the torch 300 may be oriented at any desired position so long as shielding gas can be provided in the desired position.

As the terms are used in this specification and claims, the words “generally” and “substantially” are used as descriptors of approximation, and not words of magnitude. Thus, they are to be interpreted as meaning “largely but not necessarily entirely.”

Accordingly, a preheated roller cone 10 from heating apparatus 1000 is secured to distal end 106 of robot arm 104 by chuck 120 and adapter 110. Roller cone 10 is grounded by ground cable 114, which is attached to adapter 110 at ground connector 112. Providing an electrical ground source near distal end 106 of robot 100 is necessary, since using robot 100 in the role-reversed manner of the present invention (holding the anode work piece) would otherwise result in destruction of robot 100 by arc welding the rotating components of the movable axes together. If desired, the robot 100 having torch 100′ maintains or continues to heat roller cone 10 during hardfacing.

Robot arm 104 moves in response to program control from robot controller 130 and (or) PLC 150. As stated, torch 300 is mounted to positioner 200 having two controllable axes in a substantially vertical plane. As previously mentioned, a physical indicator, such as a notch or groove, may be formed on roller cone 10 to be engaged by torch 300 to ensure proper initial orientation between torch 300, robot arm 100, and roller cone 10. Additionally, at least one position indicator is electrically connected to PLC 150 for determining location and orientation of roller cone 10 to be hardfaced relative to robot 100.

After initial orientation and positioning, transfer, plasma and shielding gas are supplied to torch 300 by their respective sources 182, 186, 190, through their respective controllers 184, 188, 192.

Torch 300 is ignited by provision of current from pilot arc power source 170 and main arc power source 172. Igniting pilot arc circuit 330 reduces the resistance to an arc jumping between roller cone 10 and electrode 304 when voltage is applied to main arc circuit 332.

Flow of hardfacing powder is provided by powder dosage system 160 dispensing controlled amounts of hardfacing powder into a conduit of flowing transport gas from transport gas source 182, having a flow rate controlled by flow controller 184. Then, relative movement, primarily of roller cone 10 relative to torch 300, as described above and below, is obtained by movement of robot arm 100 and positioner 200, permitting automated application of hardfacing 38 to the various selected surfaces of roller cone 10 in response to programming from robot controller 130 and PLC 150.

An imaging sensor 142 may be provided for identifying specific roller cones 10 and (or) parts of roller cones 10 to be hardfaced. A laser sensor 142 (FIG. 5) may also provided for determining proximity of torch 300 to roller cone 10 and tooth 20, and/or to measure thickness of applied hardfacing 38. Positioning and other programming parameters are correctable based on sensor 142 data acquisition and processing.

Robot controller 130 is primarily responsible for control of robot arm 100, while PLC 150 and data recorder provide sensor 142 data collection and processing, data analysis and process adjustment, adjustments in robot 100 movement, torch 300 oscillation, and torch 300 operation, including power, gas flow rates and material feed rates.

FIGS. 13, 13A, and 14 illustrate robot 100 manipulating a preheated roller cone 10 preheated by preheating apparatus 1000 into position to apply hardfacing material to outer end 28 of teeth 20 on outer row 16 of roller cone 10 while another robot 100 having a torch 100′ thereon (See FIG. 13A) maintains the temperature of the roller cone 10. FIG. 15 is illustrates torch 300 in position to apply hardfacing to leading flank 22 or trailing flank 24 of tooth 20 on outer row 16 of roller cone 10. FIG. 16 is an isometric view illustrating robot 100 manipulating roller cone 10 into position in preparation for application of hardfacing 38 to inner end 30 of tooth 20.

As can be seen in FIG. 6 and in FIGS. 13-16, several axes of rotation 108 of robot arm 100 provide sufficient degrees of freedom to permit vertical, horizontal, inverted, and rotated positioning of roller cone 10 beneath torch 300, allowing torch 300 to access the various surfaces of roller cone 10 while maintaining torch 300 in a substantially vertical position. In addition to providing a system and apparatus that addresses the realities of automated application of hardfacing to the complex surfaces of roller cones, the present invention provides a system and method or pattern of application of the hardfacing material to the cutters that is adapted to take advantage of the precisely controlled relative movement between torch 300 and roller cone 10 made possible by the apparatus of the present invention. These patterns will be described with reference to FIGS. 17 through 25 below.

The above-described system and method of the present invention has resolved these issues and enabled development of the method of applying hardfacing of the present invention. The present invention includes a hardfacing pattern created by superimposing a first waveform path onto a second waveform path.

FIG. 17 is a bottom view of a typical steel-tooth 20, such as might be located on roller cone 10, illustrating a first waveform target path 50 defined in accordance with the present invention. Tooth 20 has an actual or approximate included angle θ. Vertex 36 of included angle θ lies on centerline 34 of tooth 20. Centerline 34 extends through crest 26 and base 32.

As illustrated, target path 50 traverses one surface of tooth 20. By way of example, outer end surface 28 is shown, but applies to any and all surfaces of tooth 20. Target path 50 has numerous features. Target path 50 may begin with a strike path 52 located near crest 26. The various surfaces of teeth 20 are preferably welded from nearest crest 26 towards base 32, when possible, to control heat buildup.

Thereafter, target path 50 traverses the surface of tooth 20 in parallel paths while progressing in the direction of base 32. Target path 50 is comprised of traversing paths 54, which cross centerline 34, are alternating in direction, and generally parallel to crest 26.

Step paths 56 connect traversing paths 54 to form continuous target path 50. Step paths 56 are not reversing, but progressing in the direction of base 32. Step paths 56 are preferably generally parallel to the sides of the surface being hardfaced. As such, step paths 56 are disposed at an angle of approximately θ/2 to centerline 34. Taken together, traversing paths 54 and step paths 56 form target path 50 as a stationary, generally trapezoidal waveform about centerline 34, having an increasing amplitude in the direction of base 32.

The amperage of torch 300 is applied in proportion to the length of traversing path 54. This permits generation of a good quality bead definition in hardfacing 38. This is obtained by starting at the lowest amperage on traversing path 54 nearest to crest 26 of tooth 20, and increasing the amperage in proportion to the length of traversing path 54 where hardfacing 38 is being applied. The amperage of the torch can be proportionally increased as a weld path moves towards a thicker portion of the tooth.

Alternatively, amperage and powder flow are increased as hardfacing 38 is applied to crest 26. This results in increased height of the automatically welded crests 26 to their total design height. The programmed traversing paths 54 for flanks 22 and 24, inner surface 30 and outer surface 28 are also modified such that to overlap crests 26 sufficiently to create the desired profile and to provide sufficient support to crests 26 (FIG. 3).

The program sequence welds the surface of a datum tooth, then offsets around the roller cone axis the amount needed to align with the next tooth surface. Also, teeth are welded from the tip to the root to enhance heat transfer from the tooth and prevent heat buildup. Welding is alternated between rows of teeth on the roller cone to reduce heat buildup.

FIG. 18 is a schematic representation of the oscillation of torch 300. In this illustration, x-y defines a horizontal plane. Torch 300 is movable in the z-y vertical plane perpendicular to the x-y plane. The y-axis is the axis of oscillation (“AO”). Torch 300 is oscillated along the AO. The oscillation midpoint is identified as OM. Oscillation of torch 300 is controlled by instructions from programmable logic controller 150 provided to horizontal drive 204 of positioner 200. Torch 300 has a variable linear velocity along its axis of oscillation AO depending upon the characteristics of the roller cone material and the hardfacing being applied.

FIG. 19 is a schematic representation of a second waveform torch path 60 formed in accordance with the present invention. Hardfacing is applied to a tooth 20 by oscillating torch 300 while moving roller cone 10 on target path 50 beneath torch 300. In this manner, hardfacing is applied by superimposing the waveform of torch path 60 onto the waveform of target path 50. By superimposing torch path 60 onto target path 50, a superior hardfacing pattern is created. More specifically, the superimposed waveform generates a uniform and continuous hardfacing bead, is properly defined, and efficiently covers the entire surface of tooth 20 with the desired thickness of material and without excessive heat buildup.

As used throughout herein, the terms “waveform,” “trapezoidal waveform” and “triangular waveform” are not intended to be construed or interpreted by any resource other than the drawings and description provided herein. More specifically, they are used only as descriptors of the general path shapes to which they have been applied herein.

As seen in FIG. 19, torch path 60 has an amplitude Λ. It is preferred to have a Λ between 3 mm and 5 mm. It is more preferred to have a Λ is about 4 mm. Traversing path 54 (FIG. 17) is positioned in approximate perpendicular relationship to the axis of torch 300 oscillation, at the oscillation midpoint (OM). The waveform of torch path 60 is formed by oscillating torch 300 while moving roller cone 10 along traversing path 54 beneath the OM of torch 300. Thus, traversing path 54 of target path 50 becomes the axis about which the generally triangular waveform of torch path 60 oscillates.

The torch path 60 has a velocity of propagation V_(t) of between 1.2 and 2.5 mm per second at the intersection of traversing path 54 and OM of torch 300. Roller cone 10 is positioned and moved by instructions from robot controller 130 provided to robot 100. Robot 100 moves roller cone 10 to align target path 50 directly beneath the OM. Roller cone 10 is moved such that the OM progresses along target path 50 at a linear velocity (target path speed) of between 1 and 2.5 mm per second.

As illustrated, a momentary dwell period 68 is programmed to elapse between peaks of oscillation of torch 300 wherein dwell period 68 helps prevent generally triangular waveform of torch path 60 from being a true triangular waveform. Preferably, dwell period 68 is between about 0.1 to 0.4 second.

FIG. 20 is a schematic representation of the secondary oscillation 80 of traversing path 54 modifying torch path 60. Traversing path 54 is oscillated as a function of the location of oscillation midpoint OM on target path 50. Secondary oscillation 80 is created by gradually articulating roller cone 10 between step paths 56 as oscillation midpoint OM of oscillating torch 300 passes over traversing path 54. Each traversing path 54 constitutes ½λ of a wave length of secondary oscillation 80. Since traversing paths 54 are of different lengths, the wavelength of secondary oscillation 80 expands as the hardfacing application progresses towards base 32 of tooth 20. For example, where α₁ represents a first traversing path 54 and α₂ represents the next traversing path 54, α₁<α₂.

FIG. 21 is a bottom view of steel-tooth 20 illustrating traversing paths 54 connected by step paths 56 to form first waveform target path 50. Second waveform torch path 60 is superimposed on target path 50. When secondary oscillation 80 is imparted on traversing path 54, an accordion-like alteration of second waveform torch path 60 results.

Referring to FIG. 20 and FIG. 21, a maximum articulation angle of about |θ/2| of roller cone 10 occurs at each step path 56. In an optional embodiment, as oscillation midpoint OM of torch 300 progresses on each step path 56, secondary oscillation 80 is dwelled. This can be done optionally based on prior path (hardfacing) coverage of step path 56. Point 90 in FIG. 20 schematically represents the dwell periods.

As roller cone 10 moves along traversing path 54, roller cone 10 is gradually articulated by robot 100 until axis of oscillation AO (see FIG. 18) is substantially perpendicular to traversing path 54 at tooth 20 centerline 34. This occurs schematically at point 88 on FIG. 20. As roller cone 10 continues to move along traversing path 54, roller cone 10 is gradually articulated by robot 100 until step path 56 is again parallel to axis of oscillation AO. This occurs when oscillation midpoint OM arrives at a subsequent step path 56. At that point, maximum articulation of θ/2 has been imparted to roller cone 10. Oscillation is dwelled at point 90 until oscillation midpoint OM arrives at subsequent traversing path 54. Roller cone 10 is then gradually articulated back by robot 100 until traversing path 54 is again perpendicular to axis of oscillation AO at tooth centerline 34. This occurs at point 92 in FIG. 20.

Secondary oscillation of roller cone 10 continues until subsequent step path 56 is parallel to axis of oscillation AO, when oscillation midpoint OM arrives at subsequent step path 56. At that point, a maximum articulation of −θ/2 has been imparted to roller cone 10. Oscillation is again dwelled at point 90 until oscillation midpoint OM arrives at subsequent traversing path 54. It is noted that the cone can be oscillated with orientation to the torch about the z-axis of the midpoint of the torch oscillation as the cone is moved, the oscillation of the cone being a function of the cone's position on the first wave form target path.

Robot 100 rotates roller cone 10 a maximum of angle θ/2 at the intersection of traversing path 54 and step path 56, such that step path 56 and the approaching edge of tooth 20 are oriented generally parallel to axis of oscillation AO of torch 300. The waveform of torch path 60 is thus substantially modified as torch 300 approaches each step path 56. The application result is a very efficient and tough “shingle” pattern 39 of hardfacing 38 near tooth 20 centerline 34. FIG. 24 is a schematic representation of “shingle” pattern 39.

Optionally, oscillation of roller cone 10 may be dwelled when oscillation midpoint OM is near centerline 34 of tooth 20 to obtain a more uniform bead deposition across the width of tooth 20. In the preferred embodiment, step paths 56 are slightly offset from the edge of tooth 20 by a distance d.

The path speed of step path 56 may be higher than the path speed of traversing path 54, such that the amount of hardfacing deposited is controlled to provide the desired edge protection for tooth 20. It is preferred to have the length of step path 56 is greater than height Λ, and less than 2Λ. Preferably, step path 56 is approximately 5 mm. Thus, hardfacing deposited on two adjacent traversing paths 54 will overlap. Preferably, the length of overlap is about 3 mm. Generating this overlap creates a smooth surface with no crack-like defects.

Roller cone 10 may be preheated to prevent heat induced stress. When necessary, portions of the welds can be interrupted during processing to minimize and control heat buildup. Preferably, crests 26 are formed in three interrupted passes, in which the interruption provides cooling and shape stabilization of the applied material from the previous pass.

FIG. 22 is a schematic representation of another embodiment of the system and method of the present invention wherein secondary oscillation 80 of traversing path 54 again modifies torch path 60. However, in this embodiment, secondary oscillation 80 is created by relatively sudden and complete articulation of roller cone 10 at step paths 56 as oscillation midpoint OM of oscillating torch 300 reaches, or nearly reaches, step path 56. Each traversing path 54 constitutes ½λ of a wavelength of secondary oscillation 80. Since traversing paths 54 are of different lengths, the wavelength of secondary oscillation 80 expands as the hardfacing application progresses towards base 32 of tooth 20. For example, where α₁ represents a first traversing path 54 and α₂ represents the next traversing path 54, α₁<α₂.

FIG. 23 is a bottom view of steel-tooth 20 illustrating traversing paths 54 connected by step paths 56 to form first waveform target path 50. Second waveform torch path 60 is superimposed on target path 50. When secondary oscillation 80 is imparted on traversing paths 54, a herringbone pattern of hardfacing 38 is produced on the surface of tooth 20.

Referring to FIG. 22 and FIG. 23, a maximum articulation angle of about |θ/2| of roller cone 10 occurs at each step path 56 (as measured from the centerline 34 of tooth 20). In this embodiment, as oscillation midpoint OM of torch 300 progresses on each step path 56, secondary oscillation 80 is dwelled. The dwell periods are schematically represented by the high and low points of secondary oscillation 80 in FIG. 22.

As roller cone 10 moves along traversing path 54, it is not again articulated by robot 100 until oscillation midpoint OM of torch 300 nears or reaches the subsequent step path 56. This occurs schematically at point 96 on FIG. 22. At this point, roller cone 10 is articulated by robot 100 an angular amount θ, aligning subsequent step path 56 substantially parallel to axis of oscillation AO.

A traversing row 54A will comprise the centerline of a series of parallel columns of hardfacing 38 inclined at an angle to centerline 34 of tooth 20. As illustrated, the angle is approximately θ/2. Additionally, traversing row 54A will have an adjacent traversing row 54B comprising the centerline of a series of parallel columns of hardfacing 38, inclined at an angle to centerline 34 of tooth 20, where the angle is approximately −(θ/2). Still, the hardfacing 38 of traversing row 54A and the hardfacing 38 of traversing row 54B will overlap. The application result is a very efficient and tough “herringbone” pattern 41 of hardfacing 38 near tooth 20 centerline 34. FIG. 25 is a schematic representation of “herringbone” pattern 41.

As an alternative, a scooped tooth 20 configuration is obtained by welding crest 26 in two passes. The first pass adds height. When the second pass is made without pausing, hardfacing 38 applied to crest 26 adds width and laps over to the desired side.

FIGS. 26A and 26B illustrate hardfacing 38 applied using the systems and methods described herein to the cones 514 and 514′ illustrated in FIGS. 2A and 2B to provide protection to portions of cones of sintered materials using inserts 524 as teeth or cutters.

FIG. 27 illustrates hardfacing 38 applied using the systems and methods described herein to a drill bit 610, although hardfacing may be applied to any type drill bit or portions thereof as described herein.

It will be readily apparent to those skilled in the art that the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention.

Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention. 

What is claimed is:
 1. A method for depositing hardfacing material on at least one surface of a tooth of a rolling cutter, comprising: providing a pre-heating apparatus; pre-heating a rolling cutter with the pre-heating apparatus; providing a vertically oriented plasma transfer arc torch secured to a positioner having controllable movement in a vertical plane; securing the rolling cutter to a chuck mounted on an articulated arm of a robot; positioning a surface of a tooth of the rolling cutter in a substantially perpendicular relationship beneath the torch; moving the rolling cutter with the articulated arm of the robot in a plane beneath the torch in a manner providing a target path on the surface of the tooth, the target path beginning near a crest portion of the tooth and ending near a base portion of the tooth, the target path forming a first waveform about a centerline of the surface of the tooth, the target path having a plurality of tooth traversing portions substantially parallel to the crest portion of the tooth, the target path having a plurality of step paths interconnecting the plurality of tooth traversing portions, the step paths of the plurality of step paths being located at opposite edges of the surface of the tooth in an alternating fashion between subsequent tooth traversing portions of the plurality of tooth traversing portions, each step path of the plurality of step paths being parallel with the edge of the surface of the tooth at which each step path is located; oscillating the torch linearly on a horizontal axis while moving the rolling cutter with the articulated arm of the robot in the plane beneath the oscillating torch so as to impose a second torch waveform onto the first waveform on the surface of the tooth, wherein a midpoint of the torch oscillation substantially follows the target path, the second torch waveform having an amplitude such that the second torch waveform on adjacent tooth traversing portions overlaps; rotating the rolling cutter with the articulated arm of the robot in the plane beneath the torch and about the z-axis of the midpoint of the torch oscillation while the midpoint of torch oscillation follows each tooth traversing portion of the plurality of tooth traversing portions, such that: the horizontal axis is parallel with each step path of the plurality of step paths when the torch follows each step path; the horizontal axis is perpendicular to each tooth traversing portion of the plurality of tooth traversing portions when the midpoint of the torch oscillation is coincident with a midpoint of each tooth traversing portion; and the rolling cutter is rotated reciprocally at each subsequent tooth traversing portion of the of tooth traversing portions; depositing a hardfacing material on the surface of the tooth of the rolling cutter with the torch at least along the second waveform between step paths while performing the moving the rolling cutter with the articulated arm of the robot in the plane beneath the torch, in the manner providing the target path, while performing the oscillating the torch linearly on the horizontal axis and while performing the rotating the rolling cutter with the articulated arm of the robot to provide a pattern of overlapping deposited hardfacing material; and continuously heating a localized region of the rolling cutter to which hardfacing material is to be applied with a second torch of the pre-heating apparatus while depositing the hardfacing material.
 2. The method of claim 1, further comprising: measuring a voltage of a transferred arc between a torch electrode and the rolling cutter; communicating the voltage measurement data to a programmable logic controller; calculating a difference between the measured voltage and a desired voltage; calculating an arc length adjustment needed to obtain the desired voltage; and actuating the torch positioner to vertically move the arc length adjustment.
 3. The method of claim 1, further comprising: oscillating the torch in a vertical direction to maintain a substantially constant voltage output of the torch.
 4. The method of claim 1, further comprising: an amperage of the torch proportionally increased as the target path moves toward a thicker portion of the tooth.
 5. The method of claim 4, further comprising: the amperage of the torch being proportional to a length of the target path.
 6. The method of claim 1, further comprising: the oscillation of the torch along the horizontal axis having a path length of between approximately 6 mm and 10 mm.
 7. The method of claim 1, wherein moving the rolling cutter with the articulated arm of the robot in the plane beneath the oscillating torch generates a generally triangular waveform.
 8. The method of claim 1, further comprising: providing a strike path connected to the target path for initial deposition of hardfacing.
 9. The method of claim 8, wherein hardfacing material covers the crest portion and the base portion when deposited.
 10. The method of claim 1, further comprising: the traversing portions and the step paths forming a generally trapezoidal waveform about the centerline of the tooth; and wherein the first waveform has an increasing amplitude in a direction of the base portion of the tooth.
 11. The method of claim 10, further comprising: a path speed of the step path being greater than a path speed of the traversing portions.
 12. The method of claim 11, further comprising: the oscillation of the torch momentarily dwelled at an extent of oscillation.
 13. The method of claim 12, further comprising: a dwell period being between about 0.1 to 0.4 second.
 14. The method of claim 1, wherein continuously heating the rolling cutter with a second torch while depositing the hardfacing material comprises manipulating the second torch with a second robotic arm while hardfacing the rolling cutter.
 15. A method for depositing hardfacing material on at least one surface of a cutter, comprising: providing a pre-heating apparatus for heating a cutter; providing a vertically oriented plasma transfer arc torch secured to a positioner having controllable movement in a vertical plane; securing the cutter to a chuck mounted on an articulated arm of a robot; pre-heating the cutter with the pre-heating apparatus; positioning a surface of the cutter in a substantially perpendicular relationship beneath the torch with the articulated arm of the robot; moving the cutter with the articulated arm of the robot in a plane beneath the torch in a manner providing a first waveform target path on the surface of the cutter, the first waveform target path having a plurality of cutter traversing portions and a plurality of step paths interconnecting associated ones of the plurality of cutter traversing portions, the step paths of the plurality of step paths being located at opposite edges of the surface of the cutter in an alternating fashion between subsequent cutter traversing portions of the plurality of cutter traversing portions, each step path of the plurality of step paths being parallel with the edge of the surface of the cutter at which each step path is located; oscillating the torch linearly on a horizontal axis while moving the cutter with the articulated arm of the robot beneath the oscillating torch so as to impose a second torch waveform onto the first waveform target path to create a hardfacing pattern on a portion of the surface of the cutter, wherein a midpoint of the torch oscillation substantially follows the first waveform target path, the second torch waveform having an amplitude such that the second torch waveform on adjacent cutter traversing portions overlap; rotating the cutter with the articulated arm of the robot in the plane beneath the torch and about the z-axis of the midpoint of the torch oscillation while the midpoint of torch oscillation follows each cutter traversing portion of the plurality of cutter traversing portions, such that: the horizontal axis is parallel with each step path of the plurality of step paths when the torch follows each step path; the horizontal axis is perpendicular to each cutter traversing portion of the plurality of cutter traversing portions when the midpoint of torch oscillation is coincident with a midpoint of each cutter traversing portion; and the cutter is rotated reciprocally at each subsequent cutter traversing portion of the plurality of cutter traversing portions; depositing a hardfacing material on the surface of the cutter with the torch at least along the second torch waveform between step paths while performing the moving the cutter with the articulated arm of the robot in a plane beneath the torch, in the manner providing the first waveform target path, while performing the oscillating the torch linearly on the horizontal axis and while performing the rotating the cutter with the articulated arm of the robot to provide a pattern of overlapping deposited hardfacing material; and continuously heating a localized region of the cutter to which hardfacing material is to be applied with a second torch of the pre-heating apparatus while depositing the hardfacing material.
 16. The method of claim 15, wherein the second torch is an oxyacetylene torch.
 17. The method of claim 15, further comprising: pre-heating the cutter to a temperature in the range of 400° F. to 1,000° F.
 18. The method of claim 15, further comprising: maintaining a temperature of a portion of the cutter in the range of 400° F. to 1,000° F. while applying hardfacing thereto. 